1. Field
The present invention relates to a method for manufacturing panels having a decorative surface, or, so-called decorative panels. The invention also relates to a method for manufacturing paper printable with inkjet for use as a decor paper in such panels and to the paper obtainable with such method.
More particularly the invention is related to a method for manufacturing laminate panels, wherein said panels at least comprise a substrate material and a provided thereon top layer with a printed decor. The top layer is formed from thermosetting resin and one or more paper layers, wherein said paper layers comprise a decor paper having a printed pattern. The panels of the invention may relate to furniture panels, ceiling panels, flooring panels or similar, wherein these panels preferably comprise a wood based substrate, such as an MDF or HDF substrate (Medium or High Density Fiberboard) or a substrate material consisting of or essentially made of wood particleboard.
2. Related Art
Traditionally, the decor or pattern of such panels is printed on paper by means of offset or rotogravure printing. The obtained paper is taken up as a decorative paper in a so called laminate panel. According to the DPL process (Direct Pressure Laminate) the already printed paper or decorative paper is provided with melamine resin to form a decorative layer. Afterwards a stack is formed comprising at least a plate shaped substrate, said decorative layer and possibly a protective layer on top of said decorative layer, wherein said protective layer or overlay is based on resin and/or paper as well. Said stack is pressed and the press treatment results in a mutual connection or adherence of the decorative paper, the substrate and the protective layer, as well as in a hardening of the resin present in the stack. As a result of the pressing operation a decorative panel is obtained having a melamine surface, which can be highly wear resistant. At the bottom side of the plate shaped substrate a counter layer or balancing layer can be applied, or as an alternative a decorative layer might be attached to the bottom side as well, especially in the case of laminate panels for furniture. Such a counter layer or balancing layer or any other layer at the bottom side of the laminate panel restricts or prevents possible bending of the decorative panel, and is applied in the same press treatment, for example by the provision of a resin carrying paper layer as the lowermost layer of the stack, at the side of the stack opposite said decorative layer. For examples of a DPL process reference is made to the EP 1 290 290, from which it is further known to provide a relief in said melamine surface during the same press treatment or pressing operation, namely by bringing said melamine surface in contact with a structured press element, for example a structured press plate.
The printing of paper by means of an analog printing process, such as by rotogravure or offset printing, at affordable prices inevitably leads to large minimal order quantities of a particular decorative paper and restricts the attainable flexibility. A change of decor or pattern necessitates a standstill of the printing equipment of about 24 hours. This standstill time is needed for exchange of the printing rollers, the cleaning of the printing equipment and for adjusting the colors of the new decor or pattern to be printed.
Providing the printed paper with resin can lead to expansion of the paper, which is difficult to control. Problems can arise, particularly in the cases where, like in the EP 1 290 290, a correspondence between the relief and the printed decor is desired.
With the aim of restricting the costs of decorative paper and of preventing expansion, a method is known, for example from the DE 197 25 829 C1, wherein the analog printing process, for example an offset process, is used to print directly on the plate shaped substrate, whether or not with the intermediary of preparatory layers, such as melamine based layers. The printed decor is finished with melamine based layers and the created whole is cured using a pressing operation. Directly printing on the plate may lead to inferior printing quality. Any inhomogeneity internally in the plate or at its surface has a high risk of telegraphing to the upper surface, thereby forming a visual defect at the surface of the finished decorative panel. The printing process furthermore shows the same problems regarding the attainable flexibility, as when printing on paper. Finally, any quality issue on the print will result in loss of valuable board material.
Instead of analog printing techniques, digital printing techniques, especially inkjet printing technique, is becoming increasingly popular for the creation of decors or patterns, be it on paper or directly on a plate-shaped substrate possibly with the intermediary of preparatory layers. Such digital techniques can enhance the flexibility in the printing of decors significantly. Reference is made to the EP 1 872 959, WO 2011/124503, EP 1 857 511, EP 2 431 190, EP 2 293 946 and the WO 2015/118451, where such techniques are disclosed.
EP 2 132 041 discloses a method at least comprising the step of providing said paper layer with thermosetting resin and the step of providing said resin provided paper layer with at least a portion of said printed pattern. Preferably multi color printed patterns are applied for the realization of a decor, e.g. representing a wood pattern, on the abovementioned paper layer. Such decor extends over the majority, or even over the totality of the resin provided paper layer. Such a technique is known as such for example from the EP 2 132 041, where a digital printer, more particularly an inkjet printer is applied. It has however been very difficult to reliably further process such printed paper for manufacturing laminate panels, such as in a DPL process, since pressing defects may originate in the resin surface and milling, drilling or sawing through the laminate surface or at the edge thereof often leads to splitting in the top layer. Furthermore the inks or dyes of the EP'041 may overly wet the paper layer and cause wrinkling effects or bleeding upon further handling of the printed paper, leading to an instable and/or slow production process. To solve this issue the EP'041 propose to immediately dry the printed paper layer.
EP 1 044 822, EP 1 749 676 and EP 2 274 485 disclose the use of an inkjet receiver coating to enhance the printing quality on a raw decorpaper. Such inkjet receiver coating comprises pigments and a polymer such as Polyvinyl alcohol.
As recognized in WO 2015/118451 the use of paper treated with an inkjet receiver coating may lead to malfunctioning of the printing equipment. Dust may release from the inkjet receiver coating and bring about all sorts of malicious effects to the critical parts of an inkjet printer. The dust may for example clog one or more of the nozzles and lead to printing faults. WO 2015/118451 proposes to avoid too large a bent in the paper in the printing equipment to minimize the release of dust.
During private research, the inventor has also encountered problems with subsequent impregnation of dust releasing paper layers, even in the cases where the paper layers were already printed upon. The released dust may pollute the resin bath, the rollers, camera's and other equipment in, or in the immediate vicinity of, the impregnation channel, leading to defects in the final product or of the equipment used.
WO 2015/118451 further recognizes that non uniform application of the inkjet receiver coating may lead to unacceptable defects that become visible only after printing. Indeed when the inkjet receiver coating is unevenly applied, the amount of bleeding of the subsequently applied inks may vary in accordance with the distribution of the inkjet receiver coating. Typically zones of lesser print quality will be observed extending in the application direction of the coating. WO 2015/118451 proposes to alleviate this problem by also having the printed wood pattern extend with its wood nerves in the application direction, such that the inadvertent production variation may be mistaken for a natural aspect of the wood grain.